Acoustic baffle members and methods for applying acoustic baffles in cavities

ABSTRACT

An uncured acoustic absorbing member for cavity sealing comprises a thermally inert carrier ( 8, 28 ) and a thermally expandable material ( 6, 26 ) applied to the carrier ( 8, 28 ). The carrier ( 8, 28 ) contains openings ( 3 ) which become covered when the thermally expandable material ( 6, 26 ) is expanded to seal the cavity. The thermally expandable material ( 6, 26 ) may be in the form of substantially discontinuous segments ( 25 ) having an area in the range of 0.25 to 400 mm 2 . The substantially discontinuous segments ( 25 ) provide a highly uniform expansion of the material when it is thermally expanded. The acoustic absorbing members are particularly useful for sealing automotive cavities to provide acoustical abatement and to prevent the entry of fluids into the cavity.

This invention relates to acoustic baffles that have a layer of athermally expandable material, and to methods for providing acousticbaffling in cavities.

It is often desirable to seal structural cavities, particularly inautomobiles and other vehicles, to reduce the transmission of noise orvibration through the cavity or to prevent fluids from entering thecavity. One way of doing this is to introduce an expandable materialinto the cavity, and then to cause the expandable material to expand toform a foam which seals the cavity. The foam generally will be a goodabsorber of sound or other vibrations, particularly if it is a somewhatsoft material.

The expandable material is often first applied to a carrier, which isthen inserted into the cavity. The carrier provides some initialstructural support, and can provide a means for affixing the expandableposition into the portion of the cavity where it is wanted. Examples ofbaffle materials of this type are described, for example, in WO93/37506, WO 00/03894, WO 01/30906, WO 02/26549, WO 08/043,385, U.S.Pat. No. 5,385,951, EP 452 527A1, EP 1 362 683 B1 and EP 457 928 A1.

The reflective properties of the carrier material used in typicalinserts can result in noise within the cavity reflecting off the carrierinstead of being absorbed by a foam material. Many baffles consist ofeither a hard polymeric or metal carrier with the edge of the carriercovered with an expandable material. Upon cure, only the outer exteriorof the cavity wall contains absorptive material—the central crosssection of the cavity is blocked with a carrier that can reflect sound.A more effective baffle would include a soft polymer over the entiresurface of the carrier instead of only at the edges.

Another type of baffle includes a carrier covered with a die cut orinjection molded polymer on the top surface. The bottom carrier surfaceis uncovered and will exhibit poor sound absorption due to thereflection of noise by the uncovered carrier surface. If a foamablematerial were attached to the bottom surface, it would sag off duringthe expansion step and provide an uneven foam surface. A more desirableoffering would include an acoustical foam on both the top and bottom ofthe carrier.

In automotive applications, the acoustic baffle is typically insertedinto the cavity of a part which must be coated or painted. Theseautomotive coating are usually baked, and it is efficient to expand theexpandable material in the baffle at the same time that the coatingundergoes the bake cure. The problem with doing this is that the bafflegenerally blocks off the cavity even before the expansion step takesplace. This prevents the coating from penetrating into the cavity andcoating its internal surfaces. So a way is needed to allow the coatingto penetrate into the cavity, and to still seal the cavity.

An alternative type of baffle which allows for this is comprised of aporous clam shell which holds an expandable material in the cavityformed by the clam shell (EP 1 362 683 B1). Upon expansion, the cavitybecomes filled with a foam material that also encapsulates the clamshell carrier. These parts are high in mass. In addition, the amount ofassembly processes and manufacturing cost is high—the clamshell carriermust be injection molded, the expandable material must be injectionmolded or die cut, and these components then must be assembled manually.

Another problem with acoustic baffles is that the expandable materialtends to expand non-uniformly. As a result, the expanded material may bethicker in some areas than others. This leads to a loss of effectivenessin acoustic properties, as the acoustic properties of the baffle tend tobe determined by the thinnest areas of the expanded material. In somecases the expansion becomes somewhat directional, which again leads tononconformities and a loss of effectiveness. It would be desired toprovide for more uniform expansion of the expandable material in thesebaffles.

The present invention is in one aspect an uncured acoustic absorbingmember comprising a thermally inert carrier and a thermally expandablematerial applied to the carrier, wherein the carrier includes a wallportion having first and second opposing sides and openings extendingthrough the wall portion from the first opposing side to the secondopposing side, wherein said openings have a maximum dimension of from0.5 to 20 mm and wherein said openings constitute in the aggregate from10 to 85% of the surface area of the wall portion, and wherein thethermally expandable material is applied to both of said opposing sidesof the carrier such that said openings in the carrier are not filled bythe thermally expandable material, and further wherein said thermallyexpandable material expands by foaming when heated to a temperature inthe range of from 120 to 250° C. to form an expanded foam on both sidesof the carrier that covers at least 99% of the area of said openings inthe carrier.

The invention is also in certain embodiments a method of applyingacoustical baffling to a cavity, comprising

a) positioning the uncured acoustic absorbing member of the first aspecttransversely within the cavity, and

b) heating the acoustic absorbing member to a temperature of from 120 to250° C. for a time sufficient for the thermally expandable material toexpand to at least 400% of its initial volume and produce on eachopposing side of the carrier a cured foam that covers substantially theentire surface area of said opposing side of the carrier and fills atleast 99% of the area of said openings in the carrier.

The openings permit fluids to pass through the member before thethermally expandable material is expanded, while providing for acontinuous acoustic barrier and good cavity sealing after the materialhas been expanded. Therefore, in especially preferred embodiments of theforegoing process, after step a), a coating or corrosion treatment isapplied to the interior of said cavity by passing at least a portion ofthe coating through said openings in said acoustic baffle member or bydraining at least a portion of the coating or corrosion treatmentthrough said openings in said acoustic baffle member, or both, and saidcoating undergoes a thermal cure during step b).

The openings also permit the flow of gas through the member during thethermal expansion step. This can improve heat transfer, which in turncan speed the expansion of the thermally expandable material and promotegreater uniformity of the expansion.

Another benefit of this aspect of the invention is that the carrier canbe very low in mass and of a simple design. Decreasing the mass of thecarrier is beneficial in that less energy is expended on heating thecarrier during the thermal expansion set. As a result, the thermallyexpandable material can expand in less time and more uniformly. Simplecarrier designs can decrease costs. In many cases, the carrier canassume a simple planar form with openings and optionally a border and/orcertain surface features such as raised areas, as described more fullybelow.

In a second aspect, this invention is an uncured acoustic absorbingmember comprising a thermally expandable material in the form of a wallhaving first and second opposing sides and openings extending throughthe wall from the first opposing side to the second opposing side,wherein said openings have a maximum dimension of from 0.5 to 20 mm andwherein said openings constitute in the aggregate from 10 to 75% of thesurface area of the wall portion, and wherein said thermally expandablematerial expands by foaming when heated to a temperature in the range offrom 120 to 250° C. to form an expanded foam in which said openings areclosed by the expansion of the thermally expandable material.

The invention is also in certain embodiments a method of applyingacoustical baffling to a cavity, comprising

a) positioning the uncured acoustic absorbing member of the secondaspect transversely within the cavity, and

b) heating the acoustic absorbing member to a temperature of from 120 to250° C. for a time sufficient for the thermally expandable material toexpand to at least 400% of its initial volume and produce a cured foamsuch that the openings in the wall are closed by the expansion of thethermally expandable material.

In a third aspect, the present invention is an uncured acousticabsorbing member comprising a thermally inert carrier and, applied tothe carrier, a thermally expandable material which cures and expands toat least 400% of its initial volume when heated to a temperature in therange of from 120 to 250° C. to form an expanded foam, wherein thecarrier includes a wall portion having opposing surfaces, at least oneof which opposing surfaces includes raised areas which divide saidsurface into substantially discontinuous sections that each have asurface area of from 0.25 to 400 mm², and wherein at least a portion ofthe thermally expandable material is applied to at least one surface ofthe carrier within said substantially discontinuous sections defined bysaid raised areas to form a discontinuous layer of said thermallyexpandable material on said surface of the carrier.

The present invention is also a method of applying acoustical bafflingto a cavity, comprising

a) positioning the uncured acoustic absorbing member of the third aspectof the invention transversely within said cavity, and

b) heating the acoustic absorbing member to a temperature of from 120 to250° C. for a time sufficient for the discontinuous layer of thethermally expandable material to expand to at least 400% of its initialvolume and produce on at least one side of the carrier a cured foam thatcovers substantially the entire surface area of said side of thecarrier.

The discontinuous thermally expandable material of the third aspect ofthe invention has been found to expand in a highly uniform manner. Themore uniform expansion often reduces the amount of the wall surface areathat is uncovered with foam. This provides more consistent acousticalperformance, better cavity sealing and in addition can reduce the amountof the thermally expandable material that is needed to obtain goodacoustical and sealing performance.

FIG. 1 is a frontal view of an uncured acoustic absorbing member of theinvention.

FIG. 1A is a detail of a transverse member of an uncured acousticabsorbing member of the invention.

FIG. 1B is a detail of an alternate embodiment of a transverse member ofan uncured acoustic absorbing member of the invention.

FIG. 2 is a frontal view of a second embodiment of an uncured acousticabsorbing member of the invention.

FIG. 2A is a side view of a carrier for the uncured acoustic absorbingmember shown in FIG. 2.

FIG. 2B is a side view of the uncured acoustic absorbing member shown inFIG. 2.

FIG. 3 is a frontal view of a third embodiment of an uncured acousticabsorbing member of the invention.

FIG. 3A is a side view of the uncured acoustic absorbing member shown inFIG. 3.

Turning to FIGS. 1, 1A and 1B, acoustic absorbing baffle 1 includescarrier 8. In FIG. 1, carrier 8 is in the form of a lattice thatcomprises periphery 5, vertical members 2 and transverse members 4.Vertical members 2 and transverse members 4 define the wall portion ofcarrier 8. Vertical members 2 and transverse members 4 are in contactwith each other at their respective points of intersection and, togetherwith periphery 5, define openings 3 which permeate carrier 8. Thermallyexpandable material 6 is applied to at least one side of the wall formedby vertical members 2 and transverse members 4.

FIGS. 1A and 1B illustrate alternative approaches to applying thermallyexpandable material 6 to carrier 8. In the embodiment illustrated inFIG. 1A, thermally expandable material 6 encapsulates an illustrativetransverse member 4, in effect forming thermally expandable material 6onto each opposing side of the wall defined by vertical members 2 andtransverse members 4. In such an embodiment, thermally expandablematerial 6 can similarly encapsulate vertical members 2. In alternativeembodiments, vertical members 2 and transverse members 4 can be onlypartially coated with thermally expandable material 6. An example ofsuch an embodiment is shown in FIG. 1B, in which two opposing sides oftransverse member 4 (which correspond to first and second opposing sidesof the wall portion of carrier 8) are separately coated with thermallyexpandable material 6. Vertical members 6 can be similarly coated inthis embodiment.

In an alternative embodiment, carrier 8 is itself made of the thermallyexpandable material. In this case, vertical members 2 and transversemembers 4 (and optionally periphery 5) are made of the thermallyexpandable material, and no additional layer 6 is necessary.

FIGS. 2, 2A and 2B illustrate another aspect of the invention. In FIG.2, acoustic absorbing member 21 is shown positioned within a cavitydefined by structural members 29. Acoustic absorbing member 21 includescarrier 28 and thermally expandable material 26. Carrier 28 includeswall 22. Wall 22 includes first and second opposing sides, only one ofwhich is visible in FIG. 2. Each side of wall 22 includes multipleraised areas 24, which are shown in FIGS. 2, 2A and 24 as a series ofintersecting ridges. Raised areas 24 divide each surface of wall 22 intosubstantially discontinuous sections 25. Substantially discontinuoussections 25 each have a surface area of from 0.25 to 400 mm².

For purposes of this invention, sections such as sections 25 in FIG. 2are “substantially discontinuous” if (1) they are completely separatedfrom adjacent sections through raised areas, such as is shown in FIG. 3or (2) if they are separated from adjacent sections by raised areas thatextend along at least 50%, more preferably at least 75%, of theperiphery of the section. Small connections between adjacent sectionsare acceptable, although complete separation between adjacent sectionsis generally preferred. Thus, for example, ridges 24 may bediscontinuous in some embodiments, forming, for example, lines ofalternating raised and flat areas, so that adjacent sections areconnected at the points where the flat areas exist in the ridge lines.

FIG. 2A shows carrier 28 in cross-section, taken along lines 2A-2A. FIG.2B shows acoustic absorbing member 21 in cross-section, and illustrateshow thermally expandable material 26 is applied to carrier 28. Thermallyexpandable material 26 is applied to the opposing sides of wall 22,within sections 25. Ridges 24 remain uncoated or, if coated, are coatedto a very small thickness, not to exceed 50%, preferably not to exceed25%, of the height of ridges 24. In the particular embodiment shown inFIG. 2B, thermally expandable material 26 is somewhat thicker than theheight of ridges 24. It is preferred to leave ridges 24 uncoated.

An embodiment combining both aspects of the invention is shown in FIGS.3 and 3A. Acoustic absorbing member 31 is shown positioned within acavity defined by structural members 39. Carrier 38 includes wall 32 andperiphery 34. Wall 32 has first and second opposing sides, only one ofwhich is visible in FIG. 1. As shown, wall 32 contains openings 33,which, in the embodiment shown, are mainly arranged in a regulargeometric pattern. In the embodiment shown in FIGS. 3 and 3A, thermallyexpandable material 40 is applied to each side of wall 32, coveringessentially the entire surface of wall 32 except for openings 33, whichremain unfilled, and periphery 34. It is also within the scope of theinvention to apply thermally expandable material to periphery 34 ofcarrier 38.

The carrier shown in FIGS. 3 and 3A also contains raised areas. In FIGS.3 and 3A, the raised areas take the form of intersecting ridges 36 andraised opening borders 35. Ridges 36 and raised opening borders 35together define sections 37. In the embodiment shown, the height ofridges 36 and raised opening borders 35 is approximately equal to thethickness of thermally expandable material 40. As before, thermallyexpandable material 40 may have a thickness less than or somewhatgreater than the height of ridges 36 and raised opening borders 35. Inthe first and second aspects of the invention, the openings, such asopenings 3 in FIG. 1 and openings 33 in FIG. 3, each have an area offrom 0.8 to 320 mm². Preferably, the openings each have an area of from3 to 80 mm². The shape of the openings is not generally critical to theinvention and therefore can be selected arbitrarily. Therefore theopenings can be circular, elliptical, polygonal such as a triangular,rectangular, hexagonal, “crescent”-shaped, “star”-shaped or some otherconfiguration. The openings in a particular case do not need to be allthe same size or the same shape. The openings in the aggregate may coverfrom about 10 to about 85%, preferably from 20 to 60% of the surfacearea of the wall of the baffle. In FIG. 1, the openings 3 in theaggregate cover approximately 60-75% of the surface area of wall portionof carrier 8. In FIG. 3, openings 33 in the aggregate coverapproximately 20-25% of the total surface area of wall 32.

The particular arrangement of the openings also is not especiallycritical. As shown in FIGS. 1 and 3, openings 3 and 33 are arranged inpatterns of aligned columns and rows. Nearly any alternative pattern canbe used, including a random arrangement of the openings, consistent withthe mechanical integrity of the baffle prior to expansion of thethermally expandable material. It may be advantageous in some cases tolocate at least some of the openings in defined places on the wallportion of the carrier, to better provide drainage of fluids or forother reasons.

In the third aspect of the invention, the raised areas, such as raisedareas 24 in FIG. 2, ridges 36 in FIG. 3 and raised opening borders 35 inFIG. 3, may be shorter than, equal to or taller than the thickness ofthe thermally expandable material. Most preferably, such raised areasare substantially equal (+/−0.5 mm) in height to the thickness ofthermally expandable material 26. In absolute terms, the thickness ofthe raised areas are preferably from about 0.5 to 20 mm, preferably from1 to 12 mm and even more preferably from 1 to 6 mm. The substantiallydiscontinuous sections such as those indicated by reference numeral 25in FIG. 2 and reference numeral 37 in FIG. 3 each have a surface area offrom 0.25 to 400 mm², preferably from 1 to 100 mm².

In the first and second aspects of the invention, the thickness of thethermally expandable material (such as indicated by reference numerals6, 26 and 40 in FIGS. 1A, 2B and 3A, respectively) is selected togetherwith the size and number of openings and the expansion characteristicsof the thermally expandable material such that upon expansion, thethermally expandable material expands to fill at least 99%, preferably100% of the aggregate area of openings (such as openings 3 and 33 inFIGS. 1 and 3, respectively). The thermally expandable material must bethick enough, given the size and number of the openings and theexpansion characteristics of the material, that when the material isexpanded, it can fill at least 99% of the aggregate surface area of theopenings. During expansion, a thermally expandable material may expandto at least 400% of its initial volume (i.e., to a volume that is 4times that of the unexpanded layer) to as much as 3500% of its initialvolume. A preferred thermally expandable material may expand to 1000 to3000% of its initial volume, or to 2000 to 3000% of its initial volume.

In all aspects of the invention, the thickness of the thermallyexpandable material prior to expansion is generally in the range of from0.5 to 12 mm, preferably from 1 to 6 mm.

The acoustic absorbing baffle of any aspect of the invention may includeadditional functional features. Among them are attachment means such asclips 41 in FIG. 3, which can function to temporarily secure the baffleinto place in a structure until such time as the thermally expandedmaterial is expanded. In many cases, the thermally expanded materialwill serve to adhere the baffle in place once it has been expanded.

The carrier used in various aspects of the invention (such as carriers8, 28 and 38) can be made of any material that has enough mechanicalstrength to hold its shape and support the weight of the layer(s) ofthermally expandable material. The material used to make the carrier isalso thermally inert, by which it is meant that it does not melt, deformor decompose under the conditions at which the thermally expandablematerial is expanded. For example, the carrier may be made of a metal,ceramic or an organic polymer. An organic polymer may be reinforced withfibers or other reinforcing materials if necessary to provide it withthe requisite mechanical properties. Organic polymers that can be usedto make carrier 8 include high-melting thermoplastics such aspolyamides, polyimides, certain polyesters. By “high-melting” it ismeant that the thermoplastic has a melting or softening temperaturehigher than the highest temperature encountered during the expansion ofthermally expandable material.

The thermally expandable material is made of a polymeric or resinouscomposition that is a solid or highly viscous material at roomtemperature (˜25° C.), and so can be formed into a layer which isself-supporting (if no carrier is used), or, when a carrier is used,adheres to the carrier or can be adhered to the carrier though someintermediate adhesive layer. It is also possible to mechanically affixthe thermally expandable material to the carrier, but this is usuallyless preferred. The polymeric or resinous composition contains anorganic polymer or polymer-forming precursor, and a heat-activatableexpanding agent which produces a gas when subjected to a predeterminedelevated temperature. Upon heating to a temperature from 120 to 250° C.,the polymeric or resinous composition softens or melts, and theexpanding agent produces a gas. The gas forms cells in the softened ormolten polymer, which causes the thermally expandable material toincrease in volume and to form an expanded, cellular material. Theexpansion is often accompanied by a curing or crosslinking reaction toproduce a stable cellular structure in the expanded material.

The polymeric or resinous composition used to make the thermallyexpandable material may contain additional components, such asactivators, catalysts, curing agents, crosslinking agents, fillers,plasticizers, wetting agents, adhesion modifiers or tackifiers, IRabsorbers, cell openers, and the like,

Polymer and resinous compositions for making thermally expandablematerial are known. One type of thermally expandable resinouscomposition includes one or more epoxy resins and one or more epoxycuring agents, in addition to the expanding agent and other componentsas may be present. Another type of thermally expandable resinouscomposition reacts and cures to form a polyurethane or polyurea foam;such composition typically contain an isocyanate-terminated prepolymerand one or more isocyanate-reactive materials, in addition to theexpanding agent and other component as may be present. A third type ofpolymeric composition is based on a thermoplastic rubber such as astyrene-butadiene copolymer. Polymeric compositions of this type aredescribed, for example, in WO 2008/043385. Yet another type of usefulpolymeric composition is based on a polyolefin such as polyethylene or apolyethylene copolymer. Thermally expandable materials of these typesare described in U.S. Pat. No. 5,385,951, EP 452 527A1, EP 457 928 A1,WO 01/30906, WO 2007/117663, WO 2007/117664 and WO 2007/249743.

The acoustic absorbing member is conveniently prepared by pre-formingthe carrier, and applying the thermally expandable material to thepre-formed carrier. The carrier can be formed using any method that issuitable given the materials of its construction. Metal carriers areconveniently formed by a stamping method, whereas polymeric carriers aremore conveniently formed by a molding or extrusion method, followed byfurther fabrication if necessary. The thermally expandable material ismost conveniently applied through an overmolding process or an extrusionprocess, again followed by further fabrication if necessary. Anovermolding process is particularly suitable, as the mold surfaces canbe designed to provide all of the necessary surface features required ofthe thermally expandable material.

The acoustic absorbing members of the various aspects of the inventionare useful for forming acoustic and other types of baffling instructural cavities. Structural cavities of particular interest arevehicular components, in which acoustic baffling is wanted to reducenoise in passenger areas of the vehicle. Examples of such vehicularstructural cavities include the so-called A-, B- and C-pillars and roofrails of automobiles and trucks, and similar structures.

A baffle is formed by inserting the acoustic baffle member into placewithin the cavity and then heating the acoustic absorbing member to atemperature sufficient for the thermally expandable material to expand.The acoustic absorbing member is typically oriented transverse tolongitudinal dimension of the cavity. In many if not most cases, thecavity will be sealed by the baffle after the thermally expandablematerial has been expanded.

The acoustic baffle member preferably has approximately the samecross-sectional shape as the cross-sectional shape of the cavity inwhich it is to be used. The acoustic baffle member may fit snugly withinthe cavity prior to expansion of the thermally expandable material. Inthose embodiments, simple friction may be sufficient to hold theacoustic baffle member in place until the expansion step is completed.In other cases, the acoustic baffle member may be smaller incross-section than the cavity. In such cases, it is usually desirable toaffix the acoustic baffle member to the cavity to hold it in place untilthe expansion step is completed. Mechanical means such as clips, pinsand other fasteners can be used. Adhesives can be used for this purposeas well.

The thermally expandable material is expanded by heating the acousticabsorbing member to a temperature of from 120 to 250° C. A preferredexpansion temperature is from 140 to 210° C. However, the temperatureused in each particular case will of course depend on the compositionand expansion characteristics of the polymeric or resinous compositionthat makes up the thermally expandable material. Typically, thesecompositions are formulated to expand within a predetermined temperaturerange.

The heating step is continued until the thermally expandable materialexpands to form a foam having a volume at least 400% of the initialvolume of the thermally expandable material. Expansion is preferably to1000 to 3500%, more preferably from 2000 to 3000% of the initial volume.If the thermally expandable material must cross-link and/or cure duringthe expansion step, the temperature and time of the heating step arealso sufficient for those processes to occur. Typically, the heatingstep will require from 5 to 60 minutes, depending on factors such as theparticular temperature that is used, the composition of the thermallyexpandable material, the degree of expansion that is needed, thethickness of the thermally expandable material, and the thermalconductivity of the carrier.

The expanded foam will in most cases cover substantially the entiresurface area of the each side of the baffle. In embodiments of theinvention in which the carrier has openings as described herein, theexpanded foam will cover at least 99%, preferably 100% of the aggregatesurface area of such openings. Most preferably, the expanded foam willform a baffle which seals the entire cross-section of the cavity.

It is very convenient and cost-effective in many automotive vehicleassembly environments to conduct the thermal expansion step concurrentlywith the thermal cure of a coating such as an electrocoating or otherfinish that requires a bake cure. The coating often provides theassembly with protection against rust and other environmental damage.Because of this, it is important to cover all surfaces of the structure,including the inside of the cavity, with the coating material. This isfacilitated when the acoustic baffle member has openings as in the firstaspect of this invention. In such cases, the acoustic baffle member canbe inserted into the cavity at the desired location during the assemblyof the cavity or after the cavity is assembled. The coating can then beapplied to the resulting structure. The openings in the acoustic bafflemember permit the coating to flow through the cavity and contactinterior surfaces of the cavity. This is especially important when bothends of the cavity are to be sealed or when only one end of the cavityis open. Similarly, the openings in the acoustic baffle member permitexcess coating to drain easily from the part before it undergoes thebake cure.

The coated material then undergoes a heating step, during which thecoating is bake cured and the thermally expandable material is expanded.If openings are present in the acoustic baffle member, they becomecovered thermally expandable material expands and in that manner sealsthe cavity. The seal provides acoustical baffling in most cases and canalso seal the cavity to prevent liquids such as rainwater from enteringthe cavity and causing corrosion.

When the acoustic barrier member contains substantially discontinuoussections of the thermally expandable material, a benefit is often seenin that the thermally expandable material expands more uniformly thanwhen the thermally expandable material is all of a piece. It has beenfound that a certain amount of non-uniform expansion is oftenexperienced when a thermally expandable material is applied to thecarrier as a large, continuous layer. This is often the case whenovermolding methods are used to make the acoustic barrier member.Breaking the thermally expandable material into discontinuous sectionseach having a surface area of from 0.25 to 400 mm² has been found tocause a more uniform expansion of the layer. Although the invention isnot limited to any theory, it is believed that the non-uniform expansionis caused by a certain amount of non-uniform orientation that occurswhen the thermally expandable material is applied. Breaking the materialinto discontinuous sections restricts that orientation to discreteregions in the material so that, within a section, the differences inorientation are generally smaller. When the discontinuous sections areheated during the expansion step, they are better able to eliminate theremaining orientation before the expanding agent is activated, whichleads to more uniform expansion.

The expanded material will in most cases function as an acousticbarrier, whose function is to absorb, reflect or block noise andvibration that is being conducted through the cavity. The expandedmaterial usually performs well as an acoustic barrier material when itcontains mainly closed cells. Therefore, it is preferred that theexpanded material contains from 50 to 100%, preferably from 75 to 100%closed cells.

What is claimed is:
 1. An uncured acoustic absorbing member comprising athermally inert carrier and applied to the carrier a thermallyexpandable material which cures and expands to at least 400% of itsinitial volume when heated to a temperature in the range of from 120 to250° C. to form an expanded foam, wherein the carrier includes a wallportion having opposing surfaces, at least one of which opposingsurfaces includes raised areas which divide said surface intosubstantially discontinuous sections that each have a surface area offrom 0.25 to 400 mm²; and wherein at least a portion of the thermallyexpandable material is applied to at least one surface of the carrierwithin said substantially discontinuous sections defined by said raisedareas to form discontinuous sections of said thermally expandablematerial on said surface of the carrier.
 2. The acoustic absorbingmember of claim 1, wherein the carrier has first and second opposingsides and openings extending through the wall portion from the firstopposing side to the second opposing side, wherein said openings have amaximum dimension of from 0.5 to 20 mm and wherein said openingsconstitute in the aggregate from 10 to 75% of the surface area of thewall portion.
 3. The acoustic absorbing member of claim 2, wherein atleast a portion of said openings have raised opening borders.
 4. Amethod of applying acoustical baffling to a cavity, comprising a)positioning the uncured acoustic absorbing member of claim 1transversely within said cavity, and b) heating the acoustic absorbingmember to a temperature of from 120 to 250° C. for a time sufficient forthe discontinuous layer of the thermally expandable material to expandby at least 400% of its initial volume and produce on at least one sideof the carrier an expanded foam that covers substantially the entiresurface area of said side of the carrier.